全文获取类型
收费全文 | 92619篇 |
免费 | 6746篇 |
国内免费 | 6300篇 |
出版年
2024年 | 202篇 |
2023年 | 1255篇 |
2022年 | 2939篇 |
2021年 | 4871篇 |
2020年 | 3193篇 |
2019年 | 4018篇 |
2018年 | 3958篇 |
2017年 | 2870篇 |
2016年 | 4053篇 |
2015年 | 5845篇 |
2014年 | 6890篇 |
2013年 | 7249篇 |
2012年 | 8496篇 |
2011年 | 7742篇 |
2010年 | 4484篇 |
2009年 | 4187篇 |
2008年 | 4778篇 |
2007年 | 4147篇 |
2006年 | 3532篇 |
2005年 | 2821篇 |
2004年 | 2313篇 |
2003年 | 2105篇 |
2002年 | 1699篇 |
2001年 | 1471篇 |
2000年 | 1343篇 |
1999年 | 1408篇 |
1998年 | 820篇 |
1997年 | 892篇 |
1996年 | 813篇 |
1995年 | 775篇 |
1994年 | 673篇 |
1993年 | 570篇 |
1992年 | 682篇 |
1991年 | 535篇 |
1990年 | 455篇 |
1989年 | 331篇 |
1988年 | 278篇 |
1987年 | 219篇 |
1986年 | 185篇 |
1985年 | 210篇 |
1984年 | 124篇 |
1983年 | 118篇 |
1982年 | 54篇 |
1981年 | 23篇 |
1980年 | 20篇 |
1979年 | 18篇 |
1976年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
T Kubota Q Zhang J L Wrana R Ber J E Aubin W T Butler J Sodek 《Biochemical and biophysical research communications》1989,162(3):1453-1459
Metabolic labeling has revealed that rat bone cell populations in culture synthesize several forms of the secreted phosphoprotein, SppI. Most cell populations produced two major [32PO4]-labeled forms that behaved anomolously on SDS-PAGE migrating at 60 kDa and 56 kDa on 10% gels and 55 kDa and 44 kDa on 15% gels. Minor forms of intermediate sizes were also resolved. In normal bone cells the 60 kDa form was predominant and was the only form produced by the clonal bone cell line, RCA 11, whereas the 56 kDa a form predominated in the transformed bone cell line, ROS 17/2.8. In all populations [35S]-methionine-labeling revealed SppIs at approximately 60 kDa but no 56 kDa form. Each form of SppI was specifically cleaved by thrombin which generated fragments of approximately 28 kDa. Transforming growth factor beta 1 increased SppI mRNA levels 3 to 6-fold within 24 h in the normal bone cells, but no increase occurred in the ROS 17/2.8 cells. The elevated expression of SppI was reflected in a selective increase in the synthesis of the [32PO4]-and [35S]-methionine-labeled 60 kDa SppIs. 相似文献
122.
X-ray absorption spectroscopic (XAS) studies on cytochrome C1 from beef heart mitochondria were conducted to identify the effect of the hinge protein [Kim, C.H., & King, T.E. (1983) J. Biol. Chem. 258, 13543-13551] on the structure of the heme site in cytochrome c1. A comparison of XAS data of highly purified "one-band" and "two-band" cytochrome c1 [Kim, C.H., & King, T.E. (1987) Biochemistry 26, 1955-1961] demonstrates that the hinge protein exerts a rather pronounced effect on the heme environment of the cytochrome c1: a conformational change occurs within a radius of approximately 5 A from the heme iron in cytochrome c1 when the hinge protein is bound to cytochrome c1. This result may be correlated with the previous observations that the structure and reactivity of cytochrome c1 are affected by the hinge protein [Kim, C.H., & King, T.E. (1987) Biochemistry 26, 1955-1961; Kim, C.H., Balny, C., & King, T.E. (1987) J. Biol. Chem. 262, 8103-8108]. 相似文献
123.
124.
125.
126.
The effects of ethephon on stomatal resistance, water potential, osmotic potential, turgor potential, and ethylene production were determined on leaves of a drought-resistant (KS 65) and a drought-sensitive (IA 25) genotype of sorghum [Sorghum bicolor (L.) Moench] grown under wellwatered or drought-stressed conditions. With both sufficient and limited water supply, ethephon had no effect on the adaxial, abaxial, or total stomatal resistance of either genotype. For both water treatments, the adaxial stomatal resistance of the drought-sensitive genotype was higher than that of the drought-resistant genotype. Ethephon increased the amount of ethylene produced by the plants under both levels of water. For plants with sufficient water, water potentials of both genotypes were lowered by ethephon. Ethephon had no effect on the water potentials under drought or on the osmotic potentials under either water regime. With drought, the turgor potential of the drought-sensitive genotype, but not that of the drought-resistant, was increased by ethephon. 相似文献
127.
D-beta-Hydroxybutyrate dehydrogenase (BDH), a lipid-requiring enzyme, has been purified to homogeneity from rat brain using a new improved method. The purified rat brain BDH has a subunit molecular mass of 31 kilodaltons on sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The apoenzyme, i.e., the enzyme devoid of phospholipid, has no activity, but can be activated by phospholipid to a specific activity of 125 mumol/(min.mg). This is 625-fold greater than the activity in the mitochondrial fraction. The new purification procedure involves chromatography using a quaternary amine Sepharose resin followed by a sulphonate Sepharose resin, and eliminates the need for glass bead adsorption chromatography. 相似文献
128.
DNA from Guthrie spots for diagnosis of DMD by multiplex PCR 总被引:2,自引:0,他引:2
E R McCabe Y Huang M Descartes Y H Zhang R G Fenwick 《Biochemical medicine and metabolic biology》1990,44(3):294-295
129.
Sand burial effects on seed germination, seedling emergence and establishment of Panicum virgatum 总被引:5,自引:0,他引:5
Studies in the field and in a greenhouse were conducted to examine the effects of sand burial on seed germination, seedling emergence and establishment of Panicum virgatum L. on the foredunes of Lake Erie. Under natural conditions, the seedlings emerged from sand burial depths ranging from 0 to 11 cm, with a mean ± SD of 4.73 ± 1.82 cm. The frequency distribution of the depth of emergence of seedlings in the field was significantly skewed to the right and platykurtic. In the greenhouse, some seedlings emerged from a burial depth of as much as 16 cm. Although percent germination of seeds was not affected by sand burial, the percent emergence and the rate of emergence of seedlings were significantly reduced by excessive sand burial. Seedling mortality was found only among seedlings that emerged from sand burial depths of 10 cm or more. In the field, all the seedlings established in one growing season had originally emerged from sand burial depths of less than 12 cm. Within this burial range, seedlings from shallower burial depths had lower chances of establishment than expected, whereas those from deeper burial depths had higher probabilities of establishment than expected. 相似文献
130.
Role of oxidatively modified LDL in atherosclerosis 总被引:32,自引:0,他引:32
Oxidative modification of LDL is accompanied by a number of compositional and structural changes, including increased electrophoretic mobility, increased density, fragmentation of apolipoprotein B, hydrolysis of phosphatidylcholine, derivatization of lysine amino groups, and generation of fluorescent adducts due to covalent binding of lipid oxidation products to apo B. In addition, oxidation of LDL has been shown to result in numerous changes in its biologic properties that could have pathogenetic importance, including accelerated uptake in macrophages, cytotoxicity, and chemotactic activity for monocytes. The present article summarizes very recent developments related to the mechanism of oxidation of LDL by cells, receptor-mediated uptake of oxidized LDL in macrophages, the mechanism of phosphatidylcholine hydrolysis during LDL oxidation, and other biologic actions of oxidized LDL including cytotoxicity, altered eicosanoid metabolism, and effects on the secretion of growth factors and chemotactic factors. In addition, this review will examine the evidence for the presence of oxidized LDL in vivo and the evidence that oxidized LDL plays a pathogenetic role in atherosclerosis. 相似文献